Jan., 1955
SPECTR.4 O F
CiS-t?YZnSI S O M E R S O F
55
C O B a L T COGRDINATED COMPOUNDS
INFRARED ABSORPTION SPECTRA OF CIS-TRANS ISOMERS OF COORDINATION COMPOUNDS OF COBALT(II1) BY PAULE. MERRITT~ AND STEPHEN E. WIBERLES Contribution from the Walker Laboratory of Rensselaer Polytechnic Institute, Troy, N . Y . Received July 66, 1964
The infrared absorption spectra of several cis-trans pairs of coordination compounds of cobalt show specific differences between the cis and trans isomers. I n the case of the ethylenediamine-containing complexes a shift occurred in the 6.2-6.4 region of the spectrum with the trans isomer having a maximum peak a t a wave length of 0.04-0.08 p shorter than the cis Isomer. I n the case of the cis and trans isomers of the cobalt complexes containing the tetraammine group a shift occurred in the absorption band in the 12 p region with the cis isomer showing an absorption maximum at a wave length about 0.10.2 p shorter than the trans isomer. All the compounds had an absorption maximum in the 6.1-6.5p region. This band has been assigned to the (N-H) bending frequency in agreement with the assignment of Richards and Thompson.
Introduction A fundamental idea in inorganic chemistry is that coordination compounds, although numerous and of different types, have only a small number of stereochemical configurations. Recently an extremely interesting and important method for the study of the absorption spectra of compounds in the solid state was introduced by Stimson and O’Donnelle and by Scheidt.8 The introduction of this method has given great impetus to structural studies of inorganic complex coordination compounds. Although many infrared spectra of inorganic compounds have been r e p ~ r t e d ,very ~ , ~ littIe infrared work has been done to study the structure of these coordination compounds. A completely satisfactory method has not been developed for distinguishing between cis and trans isomers of metal coordination compounds of the types Ma2b2, Mazbc, M(AA)zb2 and M(AA)2bc, where a,b,c are monodentate groups, AA is a bidentate group and M is a metal. Previous workers have applied physical methods to aid in the determination of structural configurations. Holtsclaw and Sheetzs did a polarographic study of a series of cobalt complexes. Basolo’ has studied the ultraviolet region for differences in the absorption spectra of cis and trans isomers of certain coordination compounds in solution. Curran, et aZ.,8 have conducted infrared absorption studies which have been concerned with the effect of the charge of the metallic ion on the nitrogen to metal coordinate bond of complex compounds. Seng has studied the absorption spectra of inorganic complexes of glycine, and discussed their possible configurations. This study was concerned with the application of infrared absorption to aid in the differentiation between cis and trans isomers of a group of cobaltcontaining complexes. (1) Department of Chemistry, St. Lawrence University, Canton, New York. (2) M. M . Stimson and M. J. O’Donnell, J . A m . Chem. Soc., 74, 1805 (1952). (3) U.Scheidt. Z.Nalurforeck., 76, 270 (1952). (4) J. M. Hunt, M. P. Wisherd and L. C . Bonham, Anal. Chem., 92, 1478 (1950). (5) F.A. Miller and C . H. Wilkins, ibid., 24, 1253 (1962). (6) H. F. Holtzclaw, Jr., and D. P. Sheetz, J. Am. Chem. Soc., 75, 3053 (1953). (7) F. Basolo, ibid., 72,4393 (1950). (8) C. Curran, D. N. Sen, 8. Mizushima, and J. V. Quagliano, Paper 62, Pittsburgh Conference on Anal. Chem. and App. Spec., March, 1954. (9) D. N. Sen, “Infrared Studies of Some Coardination Compounds,” Ph.D. Thesis. University of Notre Dame, 1953.
Experimental Determination of Infrared Spectra.-Infrared absorption spectra were obtained with a Perkin-Elmer Model 21 double beam recording instrument and a Perkin-Elmer Model 12B. A rock-salt prism was used in both instruments except in the case of the Model 12B where a lithium fluoride prism was used for the 2 t o 4 p region in order to obtain better dispersion. The compounds were studied using the selid potassium bromide technique. About 1.5 mg. of compound was intimately ground with about 98.5 mg. of dry potassjum bromide that had been screened to 200 mesh particle size. The mixture was placed in a die constructed in this Laboratory and a rectangular sample was pressed. This sample was placed in a suitable holder and then placed in the infrared beam.
Preparation of Compounds 1 and 2 .-cis and trans-dichlorobis-( ethy1enediammine)cobalt (111) chloride were pre ared according to the method of Bailar.l0 Anal. Calcd. E r (Co(en)&l2)Cl: Go, 20.7; C1,37.3. Found: Go, 20.4; C1,37.3. 3 and 4.-cisand trans-dinitrobis-( ethylenediamine) cobalt (111) nitrate were prepared according to the method of Holtzclaw, Sheete and McCarty.ll Anal. Calcd. for ( C O ( ~ ~ ) ~ ( N O ~ ) ~Co, ) N O17.7; ~ : N, 29.1. Found: Go, 17.9; N , 29.0. 5.-Tris-(ethylenediamine)-cobalt( 111) chloride was repared by the method of Work.12 Anal. Calcd. for (en)3)Clr: Go, 17.1; C1, 30.6. .Fopnd: Go, 17.2; C1, 30.7. 6.-Carbonatobis-( ethylenediamine)-cobalt( 111) chloride was prepared by the method of Werner and Rapiport.13 And. Calcd. for (Co(en)&O3)Cl.HzO; Go, 21.5; C1, 12.9. Found: Go, 21.5; Cl, 13.1. 7.-cis-Chloroisothiocyan tobis-( ethylenediamine)-cobalt(111) thiocyanate was prepared by the method of Werner and Schmidt as given by J a ~ 0 b s e n . l ~Anal. Calcd. for (Co(en)z(NCS)Cl)SCN: Go, 17.8; N, 25.4. Found: Go, 17.5; N, 25.2. %-cis - Chloroisothiocyanatobis (ethylenediamine) - cobalt(II1) chloride was obtained as a by-product of the preparation of cis-chloroisothiocyanatobis-(ethylenediamine)-cobalt( 111) thiocyanate. It was recrystallized from hot water and air dried. Anal. Calcd. for (Co(en)z(NCS) C1)Cl: Go, 19.22; N, 22.9. Found.: Go, 19.0; N,22.8. 9 .-trans - Chloroisothiocyanatobis -(ethylenediamine)-cobalt(II1) perchlorate was prepared by the method of Werner.l6 Anal. Calcd. for (Co(en)s(NCS)Cl)C1O4: Go, 15.9; N, 18.8. Found: Go, 16.2; N, 18.6. 10.-cis Uromoaquobis (ethylenediamine) cobalt( 111) bromide was prepared by the method of Werner and Schmidt.l6 Anal. Calcd. for (Co(en)2(HrO) Br)Brr: Go, 13.6; N, 12.9. Found: Co, 13.7; N, 13.0.
ho-
-
-
-
-
(10) J. C. Bailar, Jr., “Inorganic Syntheses,“ Vol. 11. John Wiley and Sons, Inc., New York, N. Y., 1946,p. 222. (11) H . Holtzolaw, D.P. Sheetz and B. McCarty, i b i d . , Vol. IV, 1963,p. 176. (12) J. B. Work, ibid., Vol. 11, p. 221. (13) A. Werner and J. Rapiport, A n n . , 388, 72 (1912). (14) C. A. Jacobsen, “Encyclopedia of Chemical Reactions,” Vol. 111. Reinhold Publ. Corp., New York, N. Y., 1949,p. 153. (15) I b i d . , p . 154. (16) A. Werner and R. Schmidt, Ann.. 386, 136 (1412).
56
PAULE. MERRITTAND STEPHENE. WIBERLEY
VOl. 59
11.-trans - Hydroxoaquobis - (ethylenediamine) - cobalt (C-N) stretching frequency centers about the sub(111) bromide was prepared b the method of Werner and stitution of halogen atoms upon the nitrogen and Lange.17 Anal. Calcd. for &o(en),(HzO)(OH))Br2: Co, further deuteration experiments of N-monosubsti15.77; N, 15.0. Found: Co, 15.5; N, 14.8. 12 and 13.--cds- and trans-dinitrotetraaminecobalt (111) tuted amides. Lenormant21 found that the 6.4 1 bromide were prepared by the method of Biltz and Bilts.18 band in these deuterated amides was shifted to N, lower frequencies by a factor of 1.05. This indiAnal. Calcd. for ( C O ( N H ~ ) ~ ( N O ~ ) ~Co, N O ~21.1; : 35.0. Found: co,21.3; N,34.9. 14 and 15.-cis- and trans-dinitrotetraamminecobalt( 111) cated, on the basis of the work of Richards and chloride were prepared by the method of Bilte and Biltz.18 Thompson, that the assignment was better attribAnal. Calcd. for ( C O ( N H ~ ) ~ ( N O ~ ) ~Co, ) C I :23.2; C1, uted to (C-N) stretching frequency. Also, Lenor13.8. Found: C0,23.0; C1, 13.6. 16 and 17.--n’s- and trans-dichlorotetraamminecobalt- mant observed that the 6.4 p band was totally ab(111) chloride; the cis salt was prepared by taking two sent in the spectrum of N-bromoethanamide. In grams of carbonatotetraamminecobalt( 111) nitrate and dis- regard to this, Richards and Thompson noted that solving in concentrated hydrochloric acid. The purple pre- the substitution of an electrophilic group on the cipitate was filtered, washed with water and air-dried. amido-nitrogen sometimes decreases the frequency Anal. Calcd. for (Co(NH3)&12)Cl: Co, 25.3; C1, 45.6. Found: Co, 25.5; C1, 45.4%. One gram of the cis com- of this band. A band did appear at -6.0 p. Furpound was added to a small amount of water and heated ther substantiation for the assignment of this band over an open flame. The mixture changed to a green color came from Randall, et u Z . , ~ who ~ observed that this on heating. The mixture was filtered hot and the solid band was absent from the spectra of lactams. obtained contained some of the purple compound which Based on the evidence presented by Lenormant, could not be removed. Anal. Calcd. for (CO(NH~)~CIZ)and further evidence from their study of N,N-diC1: Co,25.3; C1,45.6. Found: Co,25.5; C1,45.4. 18.-Carbonatotetraamminecobalt(III) nitrate was pre- substituted ethanamides, Letaw and GroppZ4 pared by the method described by Wa1t0n.l~ A n d . Calcd. have assigned this band to the ( G N ) stretching for (CO(NH~),CO,)NO~J/ZHZO: Co, 22.8; N, 27.1. Found: frequency. Co, 22.8; N, 27.1. From the observation of the spectra of the com19.-Hexaamminecobalt(II1) chloride was prepared by the method of Bjerrum and McReyno1ds.W Anal. Calcd. pounds used in this study, evidence can be obtained for (Co( NH3)O)Cl3: Co, 22.0; C1, 39.8. Found: Co, 21.8; to support the assignment of Richards and ThompC1, 39.6.
Discussion and Results A strong absorption band appeared in the 6.16.5 p region in the spectrum of each of the nineteen compounds studied. The assignment of the group frequency with which this band is identified is quite controversial. LenormantZ1 and Randall, et u Z . , ~ ~ have argued that this band is characteristic of the amido (C-N) stretching frequency. Richards and Thompson2a and others have assigned it to the (N-H) bending frequency. The latter base their argument on the fact that primary amines absorb broadly in this region, with this band being certainly due to this deformation. I n acetamide, the frequency and the structure of this band are unchanged with respect to the primary amines. The absence of this band from the spectra of N,N-disubstituted amides and the fact that one would expect to find (N-H) bending in this region of the spectra of N-monosubstituted amides, is the basis for the assignment af this band. Richards and Thompson also studied the Raman spectra of CH3NHz and CH3ND2,and found that with the introduction of deuterium in place of the hydrogen, the (N-H) bending band was shifted to a lower frequency by a factor of 1.33-1.36. The (C-N) stretching band was shifted by a factor of 1.05. The evidence for the assignment of this band to (17) A. Werner and K. Lango, A n n , 886, 97 (1912). (18) H. Biltz and W. Biltz, “Laboratory Methods of Inorganio Chemistry,” 2nd Ed., John Wiley and Sons, Inc.. New York, N. Y., 1928, p . 179-181. (19) H.F. Walton, “Inorganic Preparations,” Prentice-Hell, Inc., New York, N . Y.,1948. (20) J. Bjerrum and J. P. McReynolds, “Inorganic Syntheses,” Val. 11, John Wiley and Sons, Inc., New York, N . Y.,p. 216. (21) H. Lenormant. Ann. chim., 5 , 459 (1950). (22) H.M. Randall, R . G . Fowler, N . Fuson, and J. R. Dangl, “Infrared Determination of Organic Structures,” D. Van Nostrand C o . , Inc., New York, N . Y., 1949. (23) R. E . Richards and H. W. Thompson, J . Chem. Soe., 1248 ( 1047).
son. As was previously pointed out, a strong band appeared in each spectrum in this region. These data appear in Table I. In this table compounds that contain both the (C-N) and (N-H) groups are listed as well as some that contain only the (NH) group. Since this band appeared in all compounds, the assignment of Richards and Thompson is more reasonable. WAVE
LENGTHOF
TABLE I BANDMAXIMUM1N 12 p REGION
.\BSORPTION ASD
Formula
SIX
12 P
6P . Reglon Wave length,
Region Wave length,
P
P
cis-[Co(en)~Cl~]Cl trans-[Co(en)zCI~]C1 cis-[Co(en)2(N02)2]N03 trans-[Co(en)2(N02)2]NOs cis-[Co(en)3]Cla d~-[Co(en)~CO~]C1~H~0 cis[Co(en)2(NCS)Cl]SCN 8 ci~-[Co(en)~(NCS)Cl]Cl 9 trans- [Co(en)*(NCS)Cl] Cl04 10 cis- [Co(en)z(H~O)Br]Br2 1 2 3 4 5 6 7
11 12
13 14 15 16 17 18 19
6.48 6.30 6.32 6.24 6.44 6.34 6.41 6.40 6.34 6.36 trans-[Co(en)~(HzO)(OH)]Br~ 6 30 cis-[Co(NHa)r( NOz)r]NOa 6.26 12.22 t~an~-[Co(NHa)q(NOs)i]NOa 6.22 12.27 c~s-[CO(NH~)((NO~)*JC~ 6.20-6.30 (b) 12.20 ~~U~S-[CO(NI-I~)~(NOZ)~]C~ 6.24 12.30 6.28 11.88 c~s-[CO(NH~)~C~~]C~ tra~~-[C~(NHa)iClz]Cl 6.24 12.06 [Co(NHa)rCOs]NOa“/2H10 6.28 12.06 [CO(NHI)BICI~ 6.46
Examination of the spectra of the groups of compounds (1-11) containing ethylenediamine as the inert constituent in the complex shows there is a (24) H. Lrtaw end A (1953).
€1. Gropp, J
Chem. P h y s . . 91, 1621
57
IKTERACTION OF GAS MOLECULES WITH CAPILLARY SURFACES
Jan., 1955
shift in the absorption band in the (N-H) bending region between the cis and trans isomer of any one compound. The absorption maxima of all compounds of the cis series appeared a t approximately the same wave length. The compounds of the trans series show absorption maxima 0.04 to 0.08 p lower. For each pair of isomers as illustrated by a typical example shown in Fig. 1, the trans isomer has a maximum that appears a t a lower wave length and a t a higher frequency than the cis isomer. This fact can be used to differentiate between the cis arid trans isomer of a given cobalt ethylenediaminecontaining complex. Although this band appeared a t approximately the same wave length in the spectrum of both the cis and trans isomer that contained four ammonia molecules as the inert constituent of the complex, a shift did occur in the broad band that appeared in the 12 p region. I n the three cases studied the maximum of this absorption band of the trans series was a t a longer wave length and a lower frequency t,han the cis isomer. The compounds of the trans series have an absorption maximum which is 0.10.2 p higher than the compounds of the cis series. This shift can be used to differentiate between the cis and trans isomers of complex inorganic compoiuids containing cobalt and the tetrammine group. Although the spectra of the cis and trans isomers of individual compounds show definite differences, the only regions showing consistent variation between the cis and trans isomer having similar groups within the complex were the 6 and 12 p regions. Acknowledgment.-The authors are indebted to
.
-_
W Dr* t , John p r.v l i d > N t"_-h p 1 1 s ~nf t"__" hCorporationJ e Mnrld 41 ,n -"--.. Y-., fnvBehr-Manning _ v _
I y
_
Perkin-Elmer Infrared Spectrophotometer.
y"-
BO
0
2
0 -.
cn
60
r"
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a
k
8 -TRANS
U
40
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6.0
MICRONS. Fig. 1.TTypical shift of abFo!:ptiop ,m?ximuy. in . 6 region using czs- ana trans-alnitronis-(etnyleneaiam1ne]cobalt(II1) nitrate as example.
THE INTERACTIOX OF GAS MOLECULES WITH CAPILLARY ,4KD CRYSTAL LATTICE SURFACES BY
w.A. sTEELE3*4AND G. D. HALSEY, ,JR,
Departnrent of Cheinistry, University of Washington, Seattle, Washington Received J u l y 27, 1964
A theory of the interaction of gas inolecules with a structureless plane has been modified to treat capillary spaces. The effect on the apparent area and energy of interaction is calculated. The interaction of a molecule with the surface of a simple cubic lattice of atoms has been computed and compared with the crude model, Experimental data on the interaction of helium, neon, argon, hydrogen, oxygen, nitrogen and methane with porous glass and saran charcoal are presented and disrussed.
1. Introduction The apparent volume V of a vessel containing a large surface area solid is given by the expression V
-
V,,, =
$"""/esp (-€/AT)- 1)dJ'
(1.1)
(1) Presented a t the 120th national meeting of the American Chemical Society, New Yotk, September 12-17, 1954. Partially supported by Contract AF19(604)-247 with the Air Force Cambridge Research Center. (2) Presented in partial fulfillment of the requirements for the 1'h.D. degree by W. A. S. (3) National Science Foundation Pre-doctoral Fellow, 1953-1954. (4) Pennsylvania State University. State College, Pa.
where E is the energy of interaction of the gas molecule with the solid, in the volume element dV. We have solved this problem previously5 for the case of an isolated plane well composed of a structureless material with a hard-sphere repulsion for the gas atom. This analysis led to a value for the distance of closest approach, the energy of intemction a t this distance and the surface area of the solid. We shall ndw consider some refined models: the problem of capillary spaces in a structureless solid, and that of the plane surface of a crystal of defi(6) W. A. Steele and G. D . Halsey, Jr., J . Chenz. P h y a . , 22, 979 (1954).
